Electric vehicle undercarriage crumple zone

ABSTRACT

A battery pack protection system is provided for use with an electric vehicle in which the battery pack is mounted under the car. The system utilizes a plurality of deformable cooling conduits located between the lower surface of the batteries within the battery pack and the lower battery pack enclosure panel. The cooling conduits are configured to deform and absorb impact energy when an object, such as road debris, strikes the lower surface of the lower battery pack enclosure panel. Further protection may be achieved by positioning a ballistic shield, alone or with a layer of compressible material, under the bottom surface of the battery pack.

FIELD OF THE INVENTION

The present invention relates generally to electric vehicles and, moreparticularly, to a system for providing undercarriage protection to anelectric vehicle.

BACKGROUND OF THE INVENTION

In response to the demands of consumers who are driven both byever-escalating fuel prices and the dire consequences of global warming,the automobile industry is slowly starting to embrace the need forultra-low emission, high efficiency cars. While some within the industryare attempting to achieve these goals by engineering more efficientinternal combustion engines, others are incorporating hybrid orall-electric drive trains into their vehicle line-ups. To meet consumerexpectations, however, the automobile industry must not only achieve agreener drive train, but must do so while maintaining reasonable levelsof performance, range, reliability, and cost.

In recent years there have been several incidents of a battery pack,either contained within a laptop computer or utilized in a vehicle,catching on fire. As a result, one of the primary issues impactingconsumer confidence with respect to both hybrid and all-electricvehicles is the risk of a battery pack fire.

Rechargeable batteries, due to their chemistries, tend to be relativelyunstable and more prone to thermal runaway than non-rechargeablebatteries. Thermal runaway occurs when the battery's internal reactionrate increases to such an extent that it is generating more heat thancan be withdrawn. If reaction rate and heat generation go unabated,eventually the heat generated becomes great enough to cause the batteryand materials in proximity to the battery to combust. Typically thermalrunaway is the result of a battery short, damage due to improper use orphysical abuse, a manufacturing defect, or exposing the cell to extremetemperatures.

Hybrid and electric vehicle (EV) manufacturers use a variety oftechniques to shield their battery packs from possible damage that mayresult from road debris or a vehicle collision. For example, in avehicle using a relatively small battery pack such as a hybrid, the packmay be protected by placing it within the rear trunk, behind the rearseats, under the front seats, or in another comparatively well protectedlocation. Vehicles utilizing large battery packs typically are forced tomount the pack under the car. To protect such a pack, a ballistic shieldmay be located between the road surface and the bottom of the pack, asdisclosed in U.S. Pat. No. 8,286,743, issued 16 Oct. 2012, and U.S. Pat.No. 8,393,427, issued 12 Mar. 2013.

Although the prior art teaches a variety of mounting techniques that caneither be used to place the battery pack in a relatively protectedregion of a car or to otherwise shield the battery pack from potentialharm, given the severity of the consequences accompanying a catastrophicbattery pack event, further techniques for protecting an undercarriagemounted battery pack are desired. The present invention provides such aprotection scheme.

SUMMARY OF THE INVENTION

The present invention provides a battery pack protection system for usewith an electric vehicle in which the battery pack is mounted under thecar. The system utilizes a plurality of deformable cooling conduitslocated between the lower surface of the batteries within the batterypack and the lower battery pack enclosure panel. The cooling conduitsare configured to deform and absorb impact energy when an object, suchas road debris, strikes the lower surface of the lower battery packenclosure panel. The deformable cooling conduits include one or morecoolant channels that may utilize either a circular or non-circularcross-section. The coolant flowing within the coolant channels flowswithin a plane that is substantially parallel to the lower battery packenclosure panel. The deformable cooling conduits may be fabricated froma plastic polymer material (e.g., polyethylene, polypropylene, etc.) andthe lower battery pack enclosure panel may be fabricated from a metal(e.g., aluminum, steel, etc.).

In one aspect, cylindrical batteries are used, for example batteriesutilizing an 18650 form factor, and positioned within the pack such thatthe cylindrical axis of each of the batteries is substantiallyperpendicular to the lower battery pack enclosure panel. The coolingconduits are interposed between the base surface of each of thebatteries and the lower battery pack enclosure panel, preferably suchthat the coolant within the coolant channels of the cooling conduitsflows within a plane that is substantially perpendicular to thecylindrical axes of the batteries.

In another aspect, a ballistic shield is mounted under the electricvehicle and under the battery pack, thus providing additional batterypack protection. The ballistic shield, which is typically fabricatedfrom either a metal or a high density plastic, is mounted at somedistance (e.g., between 1 and 15 centimeters) from the bottom of thebattery pack enclosure. A layer of a compressible material such as anopen- or closed-cell foam or an open- or closed-cell sponge may beinterposed between the battery pack and the ballistic shield.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a perspective view of a battery pack and the vehiclechassis to which it is to be mounted;

FIG. 2 provides a cross-sectional view of a portion of the battery packshown in FIG. 1;

FIG. 3 illustrates an exemplary cooling system suitable for use with thebattery pack deformable cooling conduits of the invention;

FIG. 4 illustrates an alternate exemplary cooling system suitable foruse with the battery pack deformable cooling conduits of the invention;

FIG. 5 illustrates the exemplary cooling system shown in FIG. 3 with adifferent coolant conduit configuration within the battery pack;

FIG. 6 provides the cross-sectional view of the battery pack portionshown in FIG. 2 after an object strikes the bottom of the battery packenclosure;

FIG. 7 provides the cross-sectional view of the battery pack portionshown in FIG. 2 with an alternate configuration for the deformablecooling conduits;

FIG. 8 provides the cross-sectional view of the battery pack portionshown in FIG. 2 with an alternate configuration for the deformablecooling conduits;

FIG. 9 provides the cross-sectional view of the battery pack portionshown in FIG. 2 with an alternate configuration for the deformablecooling conduits;

FIG. 10 provides the cross-sectional view of the battery pack portionshown in FIG. 9 with the addition of an underlying ballistic shield; and

FIG. 11 provides the cross-sectional view of the battery pack portionshown in FIG. 10 with the addition of a compressible layer interposedbetween the battery pack lower panel and the ballistic shield.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

In the following text, the terms “battery”, “cell”, and “battery cell”may be used interchangeably and may refer to any of a variety ofdifferent battery configurations and chemistries. Typical batterychemistries include, but are not limited to, lithium ion, lithium ionpolymer, nickel metal hydride, nickel cadmium, nickel hydrogen, nickelzinc, and silver zinc. The terms “battery pack” and “battery packenclosure” may be used interchangeably and refer to an enclosurecontaining one or more batteries electrically interconnected to achievethe desired voltage and capacity. The term “electric vehicle” as usedherein may refer to an all-electric vehicle, also referred to as an EV,a plug-in hybrid vehicle, also referred to as a PHEV, or a hybridvehicle, also referred to as a HEV, where a hybrid vehicle utilizesmultiple sources of propulsion including an electric drive system.

FIG. 1 provides a perspective view of a battery pack 101 configured tobe mounted under vehicle chassis 103. It should be understood that thepresent invention is not limited to a specific battery pack mountingscheme, battery pack size, or battery pack configuration.

FIG. 2 provides a cross-sectional view of a portion of battery pack 101.For purposes of clarity, battery interconnects and battery mounts arenot included in this view. Visible in FIG. 2 is a portion of the upperpack enclosure panel 201, a portion of the lower pack enclosure panel203, and a plurality of batteries 205. Note that the enclosure sidepanels are not shown in this view. Batteries 205 are preferablycylindrical batteries, for example batteries utilizing an 18650form-factor, and are positioned within the battery pack so that the axisof the cylinder (i.e., the cylindrical axis) is substantiallyperpendicular to both lower enclosure panel 203 and the surface of theroad. Interposed between the base of each cylindrical battery 205 andlower panel 203 are a plurality of deformable cooling conduits 207through which a liquid coolant, i.e., a heat transfer medium, is pumped.As shown, in the preferred embodiment cooling conduits 207 are alignedwith lower panel 203, resulting in the coolant within channels 209flowing in a direction substantially perpendicular to the axes of thecylindrical batteries. By regulating the flow of coolant within conduits207 and/or regulating the transfer of heat from the coolant to anothertemperature control system, the temperature of cells 205 may beregulated so that the cells remain within their preferred operatingrange.

FIGS. 3 and 4 illustrate exemplary cooling systems that may be coupledto cooling conduits 207. In system 300 shown in FIG. 3, the coolantwithin conduits 207 is pumped through a radiator 301 using a pump 303. Ablower fan 305 may be used to force air through radiator 301 to insurecooling when the car is stationary. In system 400 shown in FIG. 4, thecoolant within conduits 207 is coupled to a thermal management system401 via a heat exchanger 403. Preferably thermal management system 401is a refrigeration system and as such, includes a compressor 405 tocompress the low temperature vapor in refrigerant line 407 into a hightemperature vapor and a condenser 409 in which a portion of the capturedheat is dissipated. After passing through condenser 409, the refrigerantchanges phases from vapor to liquid, the liquid remaining at atemperature below the saturation temperature at the prevailing pressure.The refrigerant then passes through a dryer 411 that removes moisturefrom the condensed refrigerant. After dryer 411, refrigerant line 407 iscoupled to heat exchanger 403 via thermal expansion valve 413 whichcontrols the flow rate of refrigerant into heat exchanger 403.Additionally, in the illustrated system a blower fan 415 is used inconjunction with condenser 409 to improve system efficiency. It shouldbe understood that battery pack coolant conduits 207 may be coupled toother cooling/thermal management systems, and the cooling systems shownin FIGS. 3 and 4 are only meant to illustrate some common configurationsfor use with the conduits of the invention. Additionally, the geometryof cooling conduits 207 shown in FIGS. 3 and 4 is only meant toillustrate one possible configuration. For example, FIG. 5 shows thecooling system of FIG. 3 with a different conduit configuration withinbattery pack 101, one utilizing coolant manifolds. The invention may useother configurations as well, assuming that the conduits are placedbetween the batteries 205 and the lower enclosure panel 203 aspreviously described and illustrated.

Cooling conduits 207 serve a two-fold purpose. First, during normaloperation of the vehicle and the battery pack, the coolant withinconduits 207 draws heat away from batteries 205, thereby allowing thetemperature of the batteries to remain within the preferred operatingrange. Second, during a non-normal event in which an object such as roaddebris from under the vehicle strikes the bottom panel 203 of pack 101,conduits 207 help to prevent catastrophic damage to the pack byabsorbing energy through conduit deformation. As illustrated in FIG. 6,when an object under the vehicle is forced upwards in direction 601, theobject causes the bottom enclosure panel 203 to deform as well as thoseportions of conduits 207 within the strike zone. As the lower panel 203and the conduits within the strike region deform, energy is absorbed. Ifsufficient energy is absorbed through this process, damage to thebatteries 205 within the strike region can be significantly limited,thereby potentially averting a thermal runaway event. Preferablyconduits 207 are fabricated from polyethylene or a similar materialwhich is capable of severe deformation without cracking or breaking.Additionally, by selecting an electrically non-conductive coolant, ifconduits 207 do crack or break when deformed, the released coolant willnot cause a short within the battery pack.

It will be appreciated that the amount of protection provided by thebattery pack's cooling conduits can be easily tailored to meet thedesign requirements for a particular vehicle. For example and as shownin FIG. 7, by increasing the depth of the conduits, and thus theseparation distance between lower enclosure panel 203 and batteries 205,a larger deformation zone is provided. A larger deformation zone, inturn, allows an object striking the bottom of the battery pack to deformboth panel 203 and conduits 701 to a much greater extent before thebatteries are damaged. Additionally, due to the larger internal diameterof channels 703 within conduits 701, a greater degree of conduitdeformation may occur before coolant flow within the affected conduitstops completely. An added benefit of this approach is that the largerchannels within conduits 701 provide greater cooling capacity.

FIG. 8 illustrates another embodiment of the invention in which thenumber of channels 801 within each conduit 803 is increased and theshape of each channel has been changed to cylindrical. As a result, thecompression strength of the conduits has been increased, leading to aless deformable structure. At the same time, given the size of thechannels as well as the number of channels in proximity to each battery205, during a deformation event (i.e., a collision with an object) it isless likely that all cooling will be terminated for any particular cell.

FIG. 9 illustrates another embodiment of the invention. In thisembodiment both the corners of each conduit 901 and the corners of eachchannel 903 within the conduits are rounded. As a result, the largeconduit surface area in contact with the battery structures is retainedwhile still achieving a conduit which is less likely to break duringdeformation.

As previously noted, the undercarriage crumple zone of the presentinvention can be tailored to meet the specific requirements for aparticular vehicle design. Therefore a vehicle in which the battery packis very exposed, for example due to a low mounting location under thevehicle, or in which the battery pack is more likely to encounter moreroad debris, for example in a sport utility vehicle (SUV), can beprovided with more protection than a vehicle in which the battery packis less exposed or less likely to encounter road debris. Features of thecrumple zone that can be altered to achieve the desired characteristicsinclude the number of channels per conduit, width and height of theconduits, cross-sectional shape and size of each channel,cross-sectional shape and size of each conduit, conduit wall thickness(i.e., the thickness of the wall separating the channels from the outerconduit wall), conduit material, lower enclosure panel thickness, andlower enclosure panel material. Preferably the deformable coolingconduits are made from a plastic polymer such as polyethylene orpolypropylene. If desired, the material may be treated to improvethermal conductivity, while still retaining its electricallynon-conductive properties. The lower enclosure panel is preferablyfabricated from a metal such as aluminum or steel, although othermaterials may be used (e.g., a composite material).

In at least one embodiment, and as illustrated in FIG. 10, theperformance of the undercarriage crumple zone is enhanced through theinclusion of a ballistic shield 1001 mounted between the lower batterypack enclosure panel 203 and the road surface (not shown). Shield 1001absorbs some of the impact energy from road debris or other objectsprior to those objects striking the outer surface of panel 203.Furthermore, by spacing shield 1001 at some distance from panel 203 asshown in the preferred embodiment, shield 1001 is less likely to bedriven into the lower enclosure panel during a strike. Accordingly,while shield 1001 may be mounted to, and in contact with, panel 203,preferably it is spaced between 1 and 15 centimeters apart from panel203. Shield 1001 may be fabricated from a metal (e.g., aluminum),although preferably a lighter weight material such as a high densityplastic is used in order to lower vehicle weight.

FIG. 11 illustrates a modification of the embodiment shown in FIG. 10.In the illustrated embodiment, a layer of a compressible material 1101is interposed between shield 1001 and lower enclosure panel 203 to aidin impact energy absorption. Preferably layer 1101 is fabricated from anopen- or closed-cell sponge or foam, for example fabricated fromsilicone or urethane, although other similar low density materials maybe used for layer 1101. It will be appreciated that the embodimentsshown in FIGS. 10 and 11, while based on the embodiment shown in FIG. 9,can utilize any of the conduit/channel configurations described above.

It should be understood that the accompanying figures are only meant toillustrate, not limit, the scope of the invention and should not beconsidered to be to scale.

Systems and methods have been described in general terms as an aid tounderstanding details of the invention. In some instances, well-knownstructures, materials, and/or operations have not been specificallyshown or described in detail to avoid obscuring aspects of theinvention. In other instances, specific details have been given in orderto provide a thorough understanding of the invention. One skilled in therelevant art will recognize that the invention may be embodied in otherspecific forms, for example to adapt to a particular system or apparatusor situation or material or component, without departing from the spiritor essential characteristics thereof. Therefore the disclosures anddescriptions herein are intended to be illustrative, but not limiting,of the scope of the invention.

What is claimed is:
 1. A battery pack protection system, comprising: abattery pack mounted under an electric vehicle, wherein said batterypack is configured to house a plurality of batteries; and a plurality ofdeformable cooling conduits interposed between a lowermost surface ofeach of said plurality of batteries and an upper surface of a lowerbattery pack enclosure panel, wherein integral to each of said pluralityof deformable cooling conduits is at least one coolant channel, andwherein said plurality of deformable cooling conduits are configured todeform and absorb impact energy when an object strikes a lower surfaceof said lower battery pack enclosure panel.
 2. The battery packprotection system of claim 1, wherein said plurality of deformablecooling conduits are positioned within said battery pack such thatcoolant within said at least one coolant channel of said plurality ofdeformable cooling conduits flows within a plane that is substantiallyparallel to said upper surface of said lower battery pack enclosurepanel.
 3. The battery pack protection system of claim 1, wherein each ofsaid plurality of batteries utilizes a cylindrical form factor.
 4. Thebattery pack protection system of claim 3, wherein said plurality ofbatteries are positioned within said battery pack such that acylindrical axis corresponding to each of said plurality of batteries issubstantially perpendicular to said lower battery pack enclosure panel,and wherein said plurality of deformable cooling conduits are interposedbetween a base surface of each of said plurality of batteries and saidupper surface of said lower battery pack enclosure panel.
 5. The batterypack protection system of claim 4, wherein said plurality of deformablecooling conduits are positioned within said battery pack such thatcoolant within said at least one coolant channel of each of saidplurality of deformable cooling conduits flows within a plane that issubstantially perpendicular to said cylindrical axis corresponding toeach of said plurality of batteries.
 6. The battery pack protectionsystem of claim 1, wherein each of said plurality of deformable coolingconduits includes a plurality of coolant channels, and wherein each ofsaid plurality of coolant channels has a circular cross-section.
 7. Thebattery pack protection system of claim 1, wherein each of saidplurality of deformable cooling conduits includes a plurality of coolantchannels, and wherein each of said plurality of coolant channels has anon-circular cross-section.
 8. The battery pack protection system ofclaim 1, wherein each of said plurality of deformable cooling conduitsis comprised of a plastic polymer material.
 9. The battery packprotection system of claim 8, wherein said plastic polymer material isselected from the group consisting of polyethylene and polypropylene.10. The battery pack protection system of claim 1, wherein said lowerbattery pack enclosure panel is comprised of a metal.
 11. The batterypack protection system of claim 10, wherein said metal is selected fromthe group consisting of aluminum and steel.
 12. The battery packprotection system of claim 1, further comprising a ballistic shieldmounted under said electric vehicle and below said battery pack, whereinsaid ballistic shield is interposed between said battery pack and a roadsurface.
 13. The battery pack protection system of claim 12, whereinsaid ballistic shield is spaced apart from said lower battery packenclosure panel by a distance within the range of 1 centimeter to 15centimeters.
 14. The battery pack protection system of claim 12, whereinsaid ballistic shield is fabricated from a metal.
 15. The battery packprotection system of claim 12, wherein said ballistic shield isfabricated from a high density plastic.
 16. The battery pack protectionsystem of claim 12, further comprising a layer of a compressiblematerial interposed between said ballistic shield and said battery pack.17. The battery pack protection system of claim 12, wherein saidcompressible material is selected from the group of materials consistingof open-cell sponge, open-cell foam, closed-cell sponge and closed-cellfoam.